MISCELLANEOUS FERTILIZERS 203 



258. Soot. — The deposits formed in boilers and 

 chimneys when wood and soft coal are burned contain 

 small amounts -of potash and phosphoric acid. They 

 are valuable mainly as mechanical fertilizers impart- 

 ing the properties of organic matter. There is but 

 little plant food in soot, as shown by the following 

 analysis : 



Soft-coal soot. Hard-wood soot. 



Per cent. 13 Per cent. 69 



Potash O.84 I.78 



Phosphoric acid 0.75 0.96 



259. Seaweeds. — Seaweeds are rich in potash 

 and near the sea coast are extensively used for fer- 

 tilizers. 



Composition of 



mixed seaweed. 



Per cent 69 



Water 81.50 



Nitrogen 0.73 



Potash 1.50 



Phosphoric acid o. 18 



260. Strand Plant Ash. — Weeds and plants pro- 

 duced on waste land along the sea are in many Euro- 

 pean countries burned, and the ashes used as fertilizer 

 on other lands. By this means waste land is made to 

 produce fertilizer for fields which are tillable. The 

 amount of fertility removed in weeds is usually greater 

 than that in agricultural plants, because weeds have a 

 greater power of obtaining food from the soil. When 

 wheat or other grain is raised, and a small crop of 

 grain and a large crop of weeds are the result, there 

 is more fertility removed from the soil than if a heavy 



